1. Field of the Invention
This invention relates generally to an apparatus for printing identifying indicia on a work product and more particularly to such an apparatus for printing on-the-fly during an inspection or manufacturing process.
2. Related Art
In the manufacture of glass ceramic substrates for electronic circuits a large number of greensheets are stacked to form a laminate and baked in a sintering surface to form a ceramic brick. The individual greensheets are unfired ceramic sheets containing a large number of via holes and in their unfired state are flexible. Via holes are designed to have their walls coated with copper thereby forming vias or electrical conductors between two or more circuit levels. Before stacking the individual greensheets to form a laminate it is desirable to inspect each sheet for defects. An apparatus suitable for conducting such an inspection is described in co-pending patent applications Ser. Nos. 07/754,793 and 07/754,794 filed concurrently herewith and assigned to the assignee of the present invention. As part of the inspection process it is helpful to place identifying indicia on each greensheet being inspected so that sheets which must be discarded or repaired as a result of the inspection process may be readily identified by the operator. Heretofore, impact type printers have been utilized to print multiple character indicia in a single motion on a fixed greensheet. This method suffers from two disadvantages. Firstly, such impact printers use inked ribbons which are subject to loss of ink or deterioration over time resulting in degradation of print quality. Secondly, this technique creates a risk of damage to the greensheets surface due to the printing impact force.